> Btw, the concept of checksumming rows is kinda new to me.
> I needed this to store passwords on a table, so sorry if I
> cant be more help. But I am a litte bit curious, why is it
> needed? Simple checksumming (crc32/md5) does not help malicious
> changing of data, only hardware failures, but today's hardware
> has itself checksumming builtin... It probably would be a
> more point if you do some pgp/gpg style signing so you would
> get some authenticy too, but this is hard to implement right.
1.) checksumming a row will alert you when glitches have changed data. Happened twice
in 3 years to me with my previous system (with top end hardware!). This is probably
due to file system or hardware failures. There is no other way to find out whether
such a glitch has happened other than regularly checking the checksums. Despite all
progress in hardware, these errors still happen and I have these happenings well
documented. Most of the people never will notice as they do not use such a checking.
2.) We had problems before with tunneled IP connections and corrupted data. These
errors are very rare, but again, they can happen - the more complex your network setup
is, the more likely you might get a glitch or two per year. I never fou d out what to
blame: the protocol implementation, the server, the client ...
With large packet sizes, the checksumming the network protocols use is not as
collision proof as one might wish. The same crc works more reliable with small amounts
of data than with larger amounts.
3.) This checksumming helps to check whether a complex database setup with lots of
triggers and interdependencies really stores the data the way it is supposed to as you
can do the same calculation on the client and compare after commitment. Helps a lot
while testing such a setup
Horst
